Tubular incandescent halogen lamps include a helical filament axially mounted within a quartz lamp envelope. Filament supports attached to the filament support and center the filament within the lamp envelope. The ends of the lamp envelope are hermetically sealed, typically by press sealing. Molybdenum foils electrically connect the filament through the seals to external electrical leads. The interior of the lamp envelope is typically filled with an inert gas and one or more halogen compounds.
It is important to center the filament within the lamp envelope to prevent undesired interactions between the filament and the walls of the lamp envelope. In addition, it is well known that for proper lamp performance, the spacing between coils of the filament must be precisely controlled. This is important because a slight change in filament length significantly changes the operating temperature of the filament. Any change in filament temperature will have a dramatic effect on lamp performance and life.
In one particular lamp type, filament location is even more critical. This type of lamp is known as an infrared conserving lamp, which has a wavelength selective filter coating applied to the outside surface of the lamp envelope. A central region of the lamp envelope adjacent to the filament typically has a geometrically shaped section such as ellipsoidal. The selective filter coating transmits visible radiation and reflects infrared radiation back to the filament. The reflected infrared radiation can significantly reduce the electrical power consumption of the lamp. In order to gain maximum benefit from the reflected infrared radiation, the filament must be very precisely centered on the axis of the lamp envelope. Also, in order for the filament to perform at its design temperature, the filament length must be precisely controlled.
An important component of the tubular incandescent lamp capsule described above is the filament support used to support and center each end of the filament and to conduct electrical energy to the filament. Filament supports for tubular incandescent lamps are disclosed in U.S. Pat. No. 4,942,331 issued Jul. 17, 1990 to Bergman et al; U.S. Pat. No. 4,510,416 issued Apr. 9, 1985 to Meade et al and U.S. Pat. No. 4,959,585 issued Sept. 25, 1990 to Hoegler et al. Factors involved in the design of filament supports include the requirement for easy insertion in a tubular lamp envelope, which may vary in inside diameter from lamp to lamp, the requirement for accurate centering of the filament over the life of the lamp and the requirement to maintain the filament at a predetermined length throughout the life of the lamp.
It is a general object of the present invention to provide improved tubular incandescent lamp capsules.
It is another object of the present invention to provide improved filament supports for tubular incandescent lamp capsules.
It is a further object of the present invention to provide filament supports for accurate and stable centering of a filament within a tubular incandescent lamp capsule.
It is yet another object of the present invention to provide filament supports for tubular incandescent lamp capsules which are easy to manufacture and which are low in cost.